Singlet oxygen induced advanced glycation end-product photobleaching of in vivo human fingertip autofluorescence

ABSTRACT Nonenzymatic glycation and oxidation of ubiquitous proteins in vivo leads to irreversible formation of advanced glycation end products (AGEs). Due to their relatively long half life and low clearance rate AGEs tend to accumulate within static tissues and the circulatory system. Spectra ob tained using 830 nm near-infrared (NIR) excitation suggest that the so-called “autofluorescence” from al l tissues has a finite number of sources but the fact that senior and diabetic subjects produce more than other members of the general population suggests that a significant portion of the total autofluorescence from all sources originates from AGEs. Usin g pentosidine generated in a reaction mixture as described by Monnier as representative, an in vitro study unveile d very similar fluorescence and photobleaching pattern as observed for autofluorescence in vivo. A series of oxygen, air and argon purging experiments on the pentosidine-generating reaction mixture sugge sts that pentosidine is a singlet oxygen se nsitizer and secondary reactions between the pentosidine itself and/or other fluorophores and the photosensitized singlet oxygen explain the observed photobleaching. Ab initio Gaussian calculations on pentosidine reveal the ex istence of low-lying triplet excited states required for the sensitization of ground state oxygen. A commercially available product known as singlet oxygen sensor green (SOSG) that specifically serves as a singlet oxygen detection reagent confirms the generation of singlet oxygen from NIR irradiated pentosidine trimixture. This study provides one de finite chemical mechanism for understanding in vivo human skin autofluorescence and photobleaching. Keywords: Advanced glycation end products (AGEs); pentosidine; near-infrared (NIR); autofluorescence; photobleaching; singlet oxygen